Date of Award

8-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Earth Science

Advisor

Freedman, David L

Committee Member

Karanfil , Tanju

Committee Member

Lee , Cindy

Abstract

A major shift in water disinfection has been happening over the past few years from chlorination to chloramination. Chloramination is considered advantageous to chlorination due to the decreased formation of hazardous disinfection byproducts (DBPs) that are regulated by the Environmental Protection Agency (EPA) under the Disinfectants/Disinfection By-Products Rule. Despite the advantage of chloramination in generating less DBPs, unexpected increases in lead concentrations have recently been uncovered and receiving intensive attention. Because lead is neurologically toxic, research is needed to investigate the mechanisms involved in lead corrosion in such systems and to develop counteractive approaches. Currently, there is a very poor understanding of this problem. While few studies are being conducted to examine how lead leaches into drinking water systems, not enough experimental information is available on the involvement of biotic and abiotic factors in this process.
The objective of this thesis was to examine the impacts of biotic (particularly nitrifying bacteria) and abiotic factors (nitrate, nitrite, bicarbonate, sulfate, calcium, and chloride, with and without oxygen present) in drinking water distribution systems on the lead corrosion process.
The effect of nitrifying bacteria on lead corrosion was examined in this study. Significant lead corrosion occurred in a biotic treatment with a freshly cleaned lead coupon. Lead corrosion in the biotic treatment was primarily attributed to the development of a lower pH (as a result of ammonia bio-oxidation to nitrite) compared to the abiotic treatments, and the pH stayed lower through the end of experiment. Hypothesized lead corrosion factors provided by nitrification (i.e., the presence of nitrate, nitrite) were also imposed under aerobic conditions in this study. The presence of 2 ppm (as N) nitrate and nitrite increased lead corrosion in tap water. Abiotic denitrification of nitrate to nitrite, as well as further reduction of nitrite, and increasing pH occurred concurrently with lead corrosion.
Investigations of the effectiveness of nitrate and nitrite on lead corrosion under anaerobic and aerobic conditions were performed in this project. Under anaerobic conditions, the presence of nitrate (1 ppm as N) slightly increased lead corrosion, while lead corrosion increased significantly at nitrate concentration between 2 ppm and 10 ppm (as N). There was no statistically significant difference after 31 days incubation among these nitrate treatment. However, under the same conditions, the presence of nitrite (1, 2 and 5 ppm as N) inhibited lead corrosion in comparison to the DDI water control. Total lead concentration was only above the control under anaerobic conditions when the nitrite concentration was 10 ppm (as N). Abiotic denitrification of nitrate to nitrite and nitrite (presumptively to ammonia) occurred under both aerobic and anaerobic conditions. Under aerobic conditions, the presence of nitrate and nitrite did not significantly increase lead corrosion, and there were no statistical differences in total lead concentration.
The impact of several anions and cations (major components in tap water) on lead corrosion was also evaluated under aerobic conditions in this study. High bicarbonate (63 ppm), synthetic water (bicarbonate 61.6 ppm, sulfate 50.3 ppm, chloride 40 ppm, calcium 40.4 ppm and sodium 23 ppm), tap water (bicarbonate 17.6 ppm, sulfate 3.4 ppm, chloride 1.3 ppm, calcium 2.4 ppm and sodium 10.3 ppm) significantly inhibited lead corrosion compared with the DDI water control. High chloride (40 ppm), sulfate (5.4-48.7 ppm) and calcium (5-40 ppm) decreased lead corrosion in comparison to a DDI water control, but were significantly higher than the tap water. Low chloride (4.9 ppm) and low bicarbonate (11.6 ppm) significantly increased lead corrosion compared to the DDI water control.
Lead corrosion in drinking water is not only a problem of the past but also of the present. In future research, it is recommended that sufficient data be collected to allow the construction of an electron balance. This would include measurements of soluble lead and all the denitrification products. During the lead corrosion process, lead serves as an electron donor and nitrate and nitrite serve as electron acceptors. The results of this thesis provide a basis for future research on the role of nitrification in lead corrosion.

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